
//draw content
function draw() {
   canvas = getEleById('canvas')
   drawer = canvas.getContext('2d')
   drawEarth(drawer, canvas.clientWidth, canvas.clientHeight)

}

//draw Earth
function drawEarth(drawer, canvasWidth, canvasHeight) {
    var width = canvasWidth / 3;
    var height =  canvasHeight / 3;
    drawer.fillStyle = '#000'
    drawer.fillRect(0,0,width,height)
    console.log('draw earth')

}

function getEleById(id) {
    return document.getElementById(id)
}